As an angular velocity sensor aimed at reducing its cost and size, an angular velocity sensor has been developed in recent years which has a structure in which a vibrator is formed in a silicon wafer by using a MEMS (micro electro mechanical system) technique which implements miniaturization of various machine elements through the application of techniques used in semiconductor manufacturing processes etc. and in which the silicon wafer is sandwiched between two glass substrates to seal the vibrator (see, for example, Japanese Patent Application Laid-Open No. 11-264729).
FIG. 10 is a block diagram of a conventional angular velocity sensor disclosed in Japanese Patent Application Laid-Open No. 11-264729. The angular velocity sensor 60 comprises a pair of glass substrates 61 and 62 and a silicon frame 70 which is formed between both glass substrates 61 and 62 and in which a vibrator 74 including a weight 71, a base 73, and T-shaped support beams 72 is formed, and therefore the angular velocity sensor 60 has a three-layer structure of the glass-the silicon-the glass. In the upper glass substrate 61, contact holes 63 are formed and in the silicon frame 70, pillars 64 are formed so as to seal the vibrator 74 with the pillars 64 fitted to the contact holes 63. A metal is sputtered in the contact holes 63, and then the metal is subjected to wire bonding, thereby electrical connections with electrodes provided on the glass substrate 61 are established.
On the bottom surface of the glass substrate 61, a comb teeth-shaped electrode 61a for electrostatic actuation extending radially, a pair of electrodes 61b for capacitance detection, and two pairs of electrodes 61c for vibration posture control provided on both sides of the electrodes 61b for capacitance detection are provided. On the top surface of the lower glass substrate 62, a comb teeth-shaped electrode 62a for electrostatic actuation which is opposite the electrode 61a for electrostatic actuation and a pair of electrodes 62b for capacitance detection which are opposite the electrodes 61b for capacitance detection and the electrodes 61c for vibration posture control are provided. In regions corresponding to the electrodes 61a and 62a for electrostatic actuation in the top and bottom surfaces of the annular weight 71 of the vibrator 74, grooves 76 are formed radially and on the bumps and in the dips of the grooves 76, electrodes are formed. Both ends of the support beams 72 are connected to the weight 71, and the support beams 72 supports the weight 71 in a hollow portion.
When driving voltage has been applied between the electrodes of the weight 71 of the vibrator 74 and the electrodes 61a and 62a for electrostatic actuation, electrostatic forces act on the electrodes 61a and 62a for electrostatic actuation in the direction of a spacing between both electrodes, thereby the vibrator 74 vibrates while rotating about the z axis. When an angular velocity has been applied about the x axis at that time, the vibrator 74 vibrates while rotating about the y axis by the action of a Coriolis force. These vibrations vary the distances between the surface of the weight 71 of the vibrator 74 and the electrodes 61b and 62b for capacitance detection, and hence capacitances between them vary. Therefore, by detecting such variations in the capacitances, the applied angular velocity can be detected.